In her instructions, Judge Debra Nelson reminded jurors that the onus was on prosecutors to prove their case against 29-year-old George Zimmerman.

She also reminded jurors that Florida law allowed residents to use lethal force to defend themselves, under the state's controversial stand your ground law.

"The killing of a human being is justifiable and lawful if necessarily done while resisting an attempt to murder or commit a felony upon George Zimmerman, or to commit a felony in any dwelling house in which George Zimmerman was at the time of the attempted killing," Ms Nelson said.

Zimmerman's lawyer wrapped up his case by telling jurors that his client feared he was going to die when he shot Mr Martin, 17.

"He's not guilty of anything but protecting his own life," lead defence attorney Mark O'Mara said.

Zimmerman faces possible life in prison if convicted of second degree murder.

Jurors were told on Thursday that they could also consider the lesser charge of manslaughter if they were not convinced he was guilty of murder.

A manslaughter conviction, which unlike murder involves no premeditation, carries a possible maximum sentence of 30 years in prison.

The jurors had been deliberating for two hours when they asked the judge for a list of evidence in the case.

Mr O'Mara argued that prosecutors had failed to prove that Zimmerman acted with malicious intent when he pulled the trigger and fired a single, fatal shot into Mr Martin's chest.

He reminded them that Zimmerman in discussions with authorities never expressed racial animus toward Mr Martin, despite the prosecution's allegation that Zimmerman had been racially profiling Martin at the time of the shooting.

But the prosecution has argued Zimmerman stalked Mr Martin and provoked the fatal February 2012 encounter, which occurred in a gated residential community in the central Florida city of Sanford.

"He profiled him as a criminal. He assumed ... that Trayvon Martin was up to no good. And that's what led to his death," prosecutor Bernie de la Rionda told jurors in his closing arguments.

The trial has been nationally broadcast on US television, increasing anticipation and uneasiness over the verdict.

Americans have been transfixed by the courtroom drama, sending more than a million tweets each day about it.

The shooting became a cause celebre last year after authorities initially failed for several weeks to bring charges against Zimmerman, prompting some in the US civil rights community to charge that law enforcement would have pursued the case more zealously had the teenage victim been white.

There were demonstrations across the US demanding Zimmerman's prosecution, at which some protesters donned hoodie jackets similar to the one worn by Martin at the time he was shot.